1. Field of the Invention
The present invention relates to a printing machine having a printing drum onto which a stencil sheet is attached and a pressure drum clamping a print sheet. The printing machine transports the print sheet clamped by the pressure drum along the outer peripheral surface of the pressure drum, whereby the print sheet is pressed against the stencil sheet on a press portion on which the printing drum and the pressure drum press each other.
2. Description of the Related Art
A stencil printing machine as one type of printing machines is constituted so that an image on the print sheet is printed via below-described some steps.
(1) A stencil sheet is thermally perforated so as to correspond to image data.
(2) The stencil sheet thus thermally perforated is wound around and attached onto the outer peripheral surface of a printing drum.
(3) A pressure drum having a sheet clamp section is rotated synchronously with the rotation of the printing drum.
(4) The tip end of a print sheet, which is transported from a paper feed section, is clamped at a rotation upstream position of the press portion on which the printing drum and the pressure drum press each other.
(5) The print sheet thus clamped is transferred along the outer peripheral surface of the pressure drum, whereby the print sheet is transferred while the print sheet is pressed against the stencil sheet attached onto the printing drum.
(6) Ink is transferred to the print sheet in the press and transfer step (that is, (5) step).
The stencil printing machine as described above is required for the sheet clamp section of the rotating pressure drum to receive the print sheet from the paper feed section by clamping the tip end of the print sheet transferred from the paper feed section, and to take over the transportation of the print sheet. The constitution of the printing machine proposed herein is shown in FIGS. 1 and 2.
In FIGS. 1 and 2, a printing drum 100 is rotatably provided about a rotation center C1 in an arrow direction. Furthermore, a stencil sheet clamp section (not shown) clamping the tip end of a stencil sheet (not shown) is provided on the outer peripheral surface of this printing drum 100. The outer peripheral wall of the printing drum 100 is of an ink permeable structure to allow ink to be supplied from inside to the outer peripheral wall. A pressure drum 101 is rotatably provided about a rotation center C2 below the printing drum 100 in an arrow direction. A sheet clamp section 103 clamping the tip end of a print sheet 102 is provided in the vicinity of the outer peripheral surface of the pressure drum 101. The outer peripheral surfaces of the printing drum 100 and the pressure drum 101 are opposite each other, and are constituted to be capable of being pressed relatively to each other by pressing means.
A paper feed section 105 includes a primary paper feed roller (not shown) transferring only an uppermost print sheet 102 from print sheets 102 stacked on a paper feed tray (not shown), a pair of secondary paper feed rollers 106 transferring the print sheet conveyed by the primary paper feed roller toward a pressure drum side, and guide members 107 guiding the print sheet 102 transferred by the pair of secondary paper feed rollers 106 toward a predetermined rotation position on the outer peripheral surface of the pressure drum 101.
In the paper feed section 105, the printing drum 100 to which the stencil sheet is attached and the pressure drum 101 rotate synchronously with each other in the arrow direction shown in FIG. 1. As a result, the print sheet 102 is fed from the secondary paper feed rollers 106 so that the tip end of the print sheet 102 is abutted on the sheet clamp section 103 of the pressure drum 101 at timing at which the sheet clamp section 103 is located at the rotation position shown in FIG. 1 (see a two-dot chain line 102 shown in FIG. 1). Then, the sheet clamp section 103 clamps the tip end of the print sheet 102 thus fed. The clamped print sheet 102 is transferred along the outer peripheral surface of the pressure drum 101 synchronously with the rotation of the pressure drum 101. Ink is transferred onto the print sheet 102 on the press portion on which the printing drum 100 and the pressure drum 101 press each other. The sheet clamp section 103 unclamps the print sheet 102 downstream of the press portion in a rotation direction. The print sheet 102 thus unclamped is transferred to a sheet discharge section (not shown). When the sheet clamp section 103 of the pressure drum 101 arrives at the rotation position shown in FIG. 1, the above-described operation is repeated, whereby printing operation is executed in succession.
As indicated by a solid line shown in FIG. 1, however, if the tip end of the print sheet 102 is warped upward because of the curl, the material or the like of the sheet, the tip end of the print sheet 102 may possibly not be abutted on the sheet clamp section 103. Then, as shown in FIG. 2, the print sheet 102 is transferred to the portion between the pressure drum 101 and the printing drum 100 while the tip end of the print sheet 102 is not clamped by the sheet clamp section 103. If so, the print sheet 102 cannot be transferred further and sheet clogging occurs. In addition, even if the sheet clamp section 103 cannot clamp part of the print sheet 102 and the print sheet 102 is transferred to the portion between the pressure drum 101 and the printing drum 100, the tip end of the print sheet 102 may possibly be, for example, flawed, bent or creased.
The present invention has been made to solve the above-described problems. It is, therefore, an object of the present invention is to provide a printing machine capable of ensuring clamping the tip end of a print sheet by the sheet clamp section of a pressure drum and capable of preventing the flaw or the like of the tip end of the print sheet.
The first aspect of the invention provides a printing machine comprising: a printing drum around which a perforated stencil sheet is wound, and which is provided rotatably about a first axis; a pressure drum having a sheet clamp section for clamping a tip end of a print sheet, and which is provided rotatably about a second axis; and outer peripheral surfaces of the printing drum and the pressure drum, and provided to be freely pressed relatively to each other, the printing drum and the pressure drum opposite to each other on the outer peripheral surfaces, wherein the tip end of the print sheet, which is transferred from a paper feed section synchronously with rotation of both the printing drum and the pressure drum, is clamped by the sheet clamp section at a rotation clamp position upstream of a press position in a rotation direction, the printing drum and the pressure drum press each other on the press portion, the print sheet thus clamped is transferred along the outer peripheral surface of the pressure drum and the print sheet is pressed against the perforated stencil sheet on the press portion, whereby printing is conducted to the print sheet; and wherein the printing machine is provided with a sheet clamp guide member for guiding the tip end of the print sheet, which is transferred from the paper feed section, to a clamp spot of the sheet clamp section located at the rotation clamp position.
According to the first aspect of the invention, even if the tip end side of the print sheet has a curl such as an upstream warp, the tip end of the print sheet, which is transferred from the paper feed section, is guided to the clamp spot of the sheet clamp section by the clamp guide member.
The second aspect of the invention provides a printing machine according to the first aspect of the invention, wherein the sheet clamp section is divided into a plurality of segments in a direction substantially orthogonal to a sheet transfer direction; wherein guide entry spaces are provided between the divided segments of the sheet clamp section adjacent each other, respectively; and wherein the sheet clamp guide member is divided into a plurality of segments in the direction substantially orthogonal to the sheet transfer direction, and the divided segments of the sheet clamp guide member are arranged to enter the guide entry spaces, respectively, at the clamp position of the sheet clamp section.
According to the second aspect of the invention, the sheet clamp guide member guides the print sheet on the plurality of portions arranged in a direction substantially orthogonal to the sheet transfer direction of the print sheet.
The third aspect of the invention provides a printing machine according to the first aspect of the invention, wherein a guide face, opposite to the pressure drum, of the sheet clamp guide member is arranged along the outer peripheral surface of the pressure drum with a predetermined distance from the pressure drum.
According to the third aspect of the invention, the embracing angle of the sheet clamp guide member with respect to the pressure drum is wider and the stable transfer of the print sheet by the pressure drum is ensured.
The fourth aspect of the invention provides a printing machine according to the first aspect of the invention, wherein the paper feed section comprising: guide members, wherein the sheet clamp guide member is arranged on a lowest transfer downstream portion of the paper feed section, and extended from one of the guide members for guiding the print sheet by putting the print sheet between the guide members from both upper and lower directions.
According to the fourth aspect of the invention, the sheet clamp guide member surely takes over the guiding of the print sheet conducted by the guide members of the sheet feed section, or the guide members are arranged to be positioned with respect to the pressure drum, so that the positioning of the sheet clamp guide member relative to the sheet clamp section can be easily conducted.
The fifth aspect of the invention provides a printing machine according to the first aspect of the invention, wherein the sheet clamp guide member is easily bent in a direction opposite to a contact direction when the print sheet contacts with the sheet clamp guide member.
According to the fifth aspect of the invention, if the sheet clamp section clamps the tip end of the print sheet, and the print sheet thus clamped is transferred along the outer peripheral surface of the pressure drum synchronously with the rotation of the pressure drum, the print sheet contacts with the sheet clamp guide member due to the flexibility or the like of the sheet. Then, the sheet clamp guide member is easily bent in an opposite direction to a contact direction.
The sixth aspect of the invention provides a printing machine according to the fourth aspect of the invention, wherein the guide member is easily bent in a direction opposite to a contact direction when the print sheet contacts with the guide member.
According to the sixth aspect of the invention, if the sheet clamp section clamps the tip end of the print sheet, and the print sheet thus clamped is transferred along the outer peripheral surface of the pressure drum synchronously with the rotation of the pressure drum, the print sheet contacts with the guide members due to the flexibility or the like of the sheet. Then, the guide members are easily bent in an opposite direction to a contact direction.